Expansively burned ceramic material



y 1934- F. w. BUTTERWORTH ET AL -1,960,573

EXPANSIVELY BURNED CERAMIC MATERIAL Filed Feb; 10, 1933 r 14 IZUGIWS [Fan/z Wliulzerworfiz, Juan N [mag/ ag,

Patented May 29, 1934 UNITED STATES EXPANSIVELY BURNED CERAMIC MATERIAL Frank W. Butterworth, Ivan N. Doughty, and Irl R. Cline, Danville, Ill., assignors to Western Brick Company, Danville, Ill., a corporation of Illinois Application February 10, 1933, Serial No. 656,140

5 Claims. (Cl. 7237) This invention relates to a new and improved article formed by the expansive burning of clays. More particularly our invention relates to cellular articles which are formed of a predetermined size and shape.

We are aware that the expansive burning of clay has been practiced heretofore for the purpose of forming a light aggregate for the manufacture of molded articles. In all such prior processes of which we have knowledge, however, the aggregate formed is irregular in size and shape. The clay during the burning expands and even if formed before burning, the form and size are both materially altered by the expansion which is irregular in character and amount.

It is an object of the present invention to provide new and improved articles of predetermined sizes and shapes formed by the expansive burning of clays or shales.

It is also an object to provide articles of expansively burned clay which are of a desired size, shape and in which the density may also be varied as desired.

It is an additional object to provide a building block or the like which is light, strong, impervious to water, and which has high insulating properties and good sound absorption.

Other and further objects will appear as the description proceeds.

We have shown certain preferred embodiments of our invention in the accompanying drawing, in which- Figure 1 is a perspective view of one form of blank prior to burning;

Figure 2 is a similar view of the same blank after burning;

Figure 3 is a perspective view showing a modified form of blank;

Figure 4 is a transverse section showing the blank of Figure 3;

Figure 5 is a transverse section showing the blank of Figure 1 in a container before burning;

Figure 6 is a view similar to Figure 5 but showing the blank after burning; and

Figure 7 is a section similar to Figure 4 but showing a further modified form of blank.

The form of blank shown in Figure 1 consists of a rectangular blank 11 of approximately the size and general shape which it is desired the finished brick or block should take. This blank 11 is provided with a plurality of rectangular openings 12 which extend all the way through the blank. Under the expansion caused by the heat, the blank tends to swell in all directions and by the use of a container or restraining housing this swelling is limited in direction, and further the external swelling is definitely limited in amount. It will be seen that the walls about and between the openings 12 are substantially the same thickness so that the heat will be transmitted substantially uniformly to the material throughout the blank. This causes the swelling to be substantially uniform and also substantially simultaneous. When restrained by the container or housing, the blank will swell to completely fill the container and any further expansion must be effected by filling up the openings 12.

As shown in Figure 2, the block 13 is of cellular construction and the openings 12 are completely closed. Also the size of the block has slightly increased in each direction.

As shown in Figures 3 and 4, the blank 11 is enclosed in a layer of other clay or shale or simi lar material, which layer, as shown in Figure 4, may extend across one of the wide faces of the blank as well as over the sides and ends. In the form shown in Figure 7, the blank 11 is provided with a thin layer of other material which extends over the sides and ends. The outer layer of Figures 3 and 4 may be applied in any desired manner. The outer layer of Figure 7 may be applied by special dies in a usual type of extrusion machine which extrudes a continuous ribbon of stiff clay or it may be applied by other means. Either layer may be sprayed on the blank if desired.

This outer layer or coating may be of a material which is non-expanding in character, which feature will aid in preserving its continuity during the process. The coating may, if desired, also have the property of maturing at a lower temperature than the body of the blank so that a glass-like surface is produced during the burning.

One form of container or housing suitable for carrying out the method is shown in Figure 5. This container consists of a bottom 14, lateral walls 15, and a removable cover plate 16. The plate 16 may be formed with openings, which openings may approximate in form and location the openings 12 which extend through the blanks 11. The cover 16 is shown held in place by lugs 18 and wing nuts 19. The bottom 14 may be provided with openings similar to the openings of the cover 16 and located in approximate alignment with the cover openings. The container is shown as provided with the supports 20 which serve to elevate the bottom of the container above the floor 21 of the kiln or heating chamber in which the container may be placed.

In Figure 5 the blank 11 is shown in place in the container, the cover 16 being fixed in place. The openings 12 are indicated by broken lines. In Figure 6 the section shows the'block 13 after burning, this completely filling the container instead of having a small clearance on all sides as shown in Figure 4.

In forming blocks a cording to our method by the use of a container of the character shown in Figures 5 and 6, the blank is affected by the heat both through conduction through the walls of the container and by gases passing through the openings in the top and through the bottom, and through the openings 12 in the blanks until these openings have been filled by the expansion of the materiah If a container is used having no openings in the walls, the blank will be affected solely by heat conducted through the walls. It will be understood that the container may be made of any material adapted to withstand the heat required for burning the block without material injury or deformation. The container may be perforated or not, as desired. There is no very great amount of strain imparted to the container by the expansion of the block and consequently no great tensile strength is required.

It will be understood that the form of containe shown is merely illustrative, as in commercial operation it is probable that containers would be used having a plurality of compartments each of which would contain an individual block. Our process wll be described in connection with the making of bricks or building blocks although it will be understood that it may be equally well applied to articles of other forms, shapes and sizes.

The brick are made in the regular way by any of the regular processes of molding and are dried in the usual way, the only difference being that instead of being solid, they are made with voids equal to 30 to of the volume of the brick. The amount of voids will vary with different clays and according to the kind of ware to be produced. During the formation of the clay blank at the brick machine, the finest particles of clay are brought to the surface of the column or ribbon by the pressure and troweling' action of the die as the column is ejected, resulting in a. compact, dense-skinned surface. This surface may be preserved throughout the process by closely confining the blank' during the burning period, in such manner that there is substantially no expansion of the surface areas and the original surface remains intact during the burning. This dense surface is vitrified into a hard, smooth skin of very low permeability, while the interior voids provide for the expansion of the body of the unit to produce the cellular structure desired.

After these bricks or blanks which might be called hollow brick, come from the dryhouse with a large percentage of the physically combined water evaporated, they are: then placed in the 3 molds which are usually of a size just a trifle larger than the dried brick.

The process from that point on radically differs from the ordinary burning process by which the ware is contracted.

First, although the ware is theoretically dry, there is always some little moisture present and it is necessary to expose it to a temperature slightly in excess of the boiling point in order to be sure that all of the physically combined water has left it.

Second, the temperature is then increased to a point well below the dehydrating and oxidation points.

Third, immediately that the ware has attained the above temperature, it is put into a temperature appreciably higher than that at which it vitrifies or at which the fluxes melt. The effect of this is to melt the fluxes and at the same time, expel the gases contained in the clay, resulting in a rapid and more or less thorough expansion of the ware. The ware being enclosed in and nearly filling a mold of the ultimate size and shape of the desired ware, and the clay body being full of voids, the expansion goes mainly in one direction; that is, toward the voids which are either entirely or partially filled up.

Fourth, the ware is kept at this temperature for a very short time, sufficiently long to insure a vitrification of all of the partitions forming the cells in which the gases are trapped, and although the major part of theexpansion comes quickly, the expansion will continue for an indefinite period if this high temperature is maintained.

Fifth, the ware is then cooled in the regular way, although our experience is that due to its cellular properties, etc. it can be cooled much quicker without danger than where it is contracted during the burning process.

It has been found that the time required for this method of burning after the physically combined water has been expelled and up to the time of cooling is often as little as fifteen minutes, dependent upon'the character of ,zthe clay, the maximum temperature of the hot zone and the number and volume of the voids in the unit.

As a specific example, the blank may be placed in a temperature of approximately 1000 F. and the temperature gradually raised until in twenty-five minutes it reaches 2000 F. The rise in temperature may continue until at the end of forty minutes it reaches a maximum of 2240" R, which is maintained for three minutes after which the block is slowly cooled.

By our method, the amount of expansion can be exactly controlled by the temperature of the hot zone and the length of time in which the ware is allowed to remain at the high temperature point. Thus, from the same material, ware of very great strength and considerable density can be made; or, ware of little structural strength and extremely cellular can be manufactured.

If it is desired to retain somewhat the same outside appearance of the ware as though it were burned by the ordinary process, the dry hollow ware is made so that there will be very little clearance between it and the mold; and the mold is not perforated. By maintaining this close juxtaposition of the surface of the blank and the wall of the container, the original texture and condition of the ware is maintained, even though the expansion is 200%. v

Although it seems desirable to form the ware in the usual way as described above, we have found that the following method also produces the same kind of ware. In the place of the regular molding machinery, the raw shale after being ground to fairly uniform particles, say that will pass through a ring and be retained on a screen with the holes in diameter are coated in a drum or any other apparatus'with a coating of a rather weak solution of sodium silicate and while wet, these particles of clay are lightly pressed together in the desired form with voids and the sodium silicate allowed to set, after which the ware is treated in the same way as formerly described. The sodium silicate will make a bond between the particles, holding them together in the desired form and this bond will not be destroyed by heat until a temperature is reached at which another bond is substituted. By either process the resulting ware is highly cellular and therefore is very light in weight, it being quite possible in the same clays and shales to secure 200% expansion; that is, the clay or shale will have been converted into a cellular mass three times its original volume.

This ware, burned in this way, as stated above, can be made sufficiently dense to have high 1,960,573 crushing strength and still be cellular or can be.

expanded to almost the entire limit into a very lightweight ware with but little structural strength.

The containers or molds may be knock-down in character or may be slightly tapered to facilitate the removal of the formed blocks. Various means may be used for preventing or limiting adhesion of the formed block to the container. For example, the'interior of the container may be coated with graphite or a lime wash, or may be sanded, as is customary in forming various types of bricks and blocks from clay. As an alternative, a refractory sand may be rolled into the surfaces of the blanks. As another means of preventing adhesion, the blank may be enclosed in paper or the container lined with paper. This paper will, of course, turn to ash under the heat of the burning, but the non-fusible ash will serve to prevent adhesion. Sand used in the mold to prevent adhesion might also aid in giving a desired finish to the block, as is customary in various types of face brick at the present time. As a further method of preventing adhesion and giving a desired surface, a paper or membrane having sand caused to adhere thereto by an adhesive such as sodium silicate, may be used for lining the container, the paper or membrane being destroyed by the heat and the sand adhering to the finished block.

It Will be further understood that the form of blank shown in Figure l is also merely illustrative, as a large variety of forms of blank may be usedto meet varying conditions and requirements. The openings extending through the block may vary in size and location, and when the block is burned they may be fully or partially closed up as desired. For many purposes for which these blocks are adapted it is immaterial, or in some cases desirable, to have openings extending through the blocks. In such cases the perforations or openings through the blank mayv only partially be filled by the expansion. In cases where it is desired to have openings through the finished block which openings are of a definite 1 size and character, collapsible or removable mold members or cores may be placed in the container extending through the blank and remaining in place until the heat treatment is completed.

The amount of expansion permitted upon the outside of' the blank will vary as desired. In some cases it may be desirable to limit this expansion very closely and force all of the expansion to the interior of the block. Such a method of manufacture will tend to give a smoother and denser surface than where greater exterior surface expansion is permitted. The surface may be treated in various ways as is now known in the ceramic art .by having layers of different types of clay-or other material placed on the blanks before burning,'as shown in Figures 3, 4 and 7, in order to give any desired finish to the surface of the product. The surface color and texture may be varied by permitting more or less surface oxidation before the burning temperature reaches that necessasry for causing the cellular expansion.

Where the blanks are formed by cutting them from'a ribbon or column extruded from dies, they will have four denser surfaces. Where these four surfaces are closely confined in the container during burning the finished surfaces have been found to be very resistant to water penetration. These four surfaces, are those of which one or more will be exposed when the blocks are built into a wall in the usual way. The dense surfaces have been tested for water absorption under a head of about one foot of water and the absorption has been found to be only about oneteenth of an inch per twenty-four hours. The total water absorptive capacity of the blocks is only about fifteen percent by weight and while thisabsorption may be reached in about seventytwo hours by immersing the blocks and thus exposing the less dense surfaces, it is not reached for about two weeks if only the denser surfaces are exposed to water.

The amount of expansion may be controlled by the nature of the material forming the blank, by its moisture content, by the speed with which the blank is moved through the various heat zones,

and by the modification of the temperatures of these zones. By variation of any or all of these elements a block of desired lightness and cell size and content may be obtained.

The kiln or furnace in which this burning takes place can be of any type but in our practice we prefer a tunnel furnace, with the ware moving through a hot zone either on cars according to usual tunnel kiln practice, or on a refractory conveying system. Due to the short time in which the ware is in the hot zone (this may be from three to ten minutes), the ware is produced very rapidly and the burning cost greatly reduced over any other known process.

Whilewe have described and shown various methods of carrying out our invention, these are to be understood as illustrative only, as both method and product are capable of wide variation to meet differing requirements and we contemplate such changes' and modifications as come within the spirit and scope of the appended claims.

We claim:

1. An expanded argillaceous article of predetermined size and shape having its exterior comprising non-expanded burned surfaces, and expanded burned surfaces, the body of the block being of an interiorly expanded cellular structure.

.2. An expanded argillaceous block of predetermined size and shape, said block having its exterior consisting of burned surfaces, four of the surfaces being dense and smooth, the body of the block being of an interiorly expanded cellular structure, and the remaining two surfaces being relatively porous.

3. An expanded argillaceous block of predetermined size and shape, said block having its exterior consisting of burned surfaces, four of the surfaces being non-expanded, dense and smooth and the remaining two surfaces being relatively porous, the body of the block being of an interiorly expanded cellular structure, the portions of the body of the block adjacent the dense surfaces being more dense than other portions of the block. 4. An expanded ceramic block formed of interiorly expanded burned argillaceous material, and a non-expanded facing burned integral with the expanded portion.

5. An expanded ceramic block formed-of interiorly expanded burned argillaceous material, and a non-expanded facing burned integral with the expanded portion, the expanded portion having more dense parts adjacent the non-expanded facing. I

FRANK W. BUTTERWORTI-I. IVAN N. DOUGHTY. IRL R; CLINE. 

